USE OF LARVAL STOCKING IN RESTORATION OF CHESAPEAKE BAY STRIPED BASS

After the collapse of striped bass Morone saxatilis stocks in the late 1970s, hatchery programs and release experiments were instituted to e valuate the potential to restore striped bass in Chesapeake Bay. Becau se survival of striped bass larvae to first feeding (7 d after hatch) is low in Chesapeake tributaries, ranging from 0.2 to 5.2% of eggs spa wned, it is possible to enhance survival through hatchery propagation of eggs and yolk-sac larvae, and it may be feasible to supplement recr uitment by stocking post-yolk-sac larvae. During 1991-1993, otoliths o f 31.7 million hatchery-produced striped bass larvae (5-13 d after hat ch) were chemically marked and released into two tributaries of Chesap eake Bay. In years of moderate to poor natural larval production (1991 , 1992), stocked larvae contributed 20 to 30% to overall juvenile abun dance. In 1993, a year of high natural production, stocked larvae cont ributed only 5% to juvenile abundance, although numbers contributed we re higher than in previous years. Using field and hatchery estimates o f larval and juvenile growth and mortality, enhancement strategies wer e compared in which fish were released at three different ages: larvae (7 d post-hatch), summer-stocked juveniles (55 d post-hatch), or fall -stocked juveniles (220 d post-hatch). Based upon hatchery records, re ared larvae and juveniles experienced substantially higher rates of gr owth and survival than did wild larvae and juveniles of similar age. I n years of low natural egg production, cohort biomass at 220 d post-ha tch was highest when juveniles were stocked in summer or fall. When ap proximate costs were incorporated into the analysis, the efficacy of s tocking 7-d-old larvae was higher than summer and fall stocking of juv eniles if stocked larvae encountered favourable conditions. In years o f poor natural recruitment, stocking post yolk-sac larvae into estuari ne tributaries could supplement stocks of striped bass and possibly ot her anadromous species which experience high embryo and yolk-sac larva mortality. (C) 1998 International Council for the Exploration of the Sea.